Magnetic head positioning mechanism

ABSTRACT

A magnetic head positioning mechanism is provided which is excellent in shock-resistance and can achieve high positioning accuracy. By constructing the magnetic head positioning mechanism so that a fine actuator section is composed of an actuator spring made from a thin steel plate, a base plate made from a thick steel plate to be junctioned to the actuator spring, stiffness of the fine actuator section in a vertical direction can be improved with flexibility of a driving spring section mounted on the actuator spring being still kept, that is, with sufficient positioning accuracy and satisfactory stroke being maintained. Moreover, by designing a strength of the fine actuator section so that the actuator spring and a holder arm do not overlap when the base plate is connected to the holder arm, the fine actuator section can be made thin and implementing of the fine actuator section among narrow plates in a positioning device is made easy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an improved magnetic head positioningmechanism for disk devices including magnetic disks or optical disks.

The present application claims the priority of Japanese PatentApplication No. Hei11-305440 filed on Oct. 27, 1999, which is herebyincorporated by reference.

2. Description of the Related Art

Recording density of magnetic disks is increasing at a rate of 60% ormore annually as technology to increase a BPI (Bit Per Inch) and/or TPI(Track Per Inch) improves. In order to implement high BPI devices, inaddition to a reduction in an amount of floating of a magnetic head,introduction of the magnetic head with high sensitivity andhighly-efficient signal processing, technology of positioning themagnetic head with high accuracy is required.

In a case of the recording density of 1 Gb/in², for example, density ina direction of a track is 8 kTPI or less and its track pitch is about 3μm to 4 μ. However, to obtain the recording density of 10 Gb/in², sinceits track density has to be 25 kPTI or more and its track pitch has tobe 1 μm or less, a magnetic head positioning accuracy of 0.1 μm or less(being equivalent to about 10% of the track pitch) is needed.

FIGS. 14A, 14B, 14C and 15 show a conventional magnetic head positioningmechanism used in magnetic disk devices. As shown in FIGS. 14A and 14B,a magnetic head supporting section (suspension) 5 is composed of agimbal spring 3 to hold a slider 2 on which a magnetic head is mounted,a load beam 4 to impose a predetermined pressing load on the slider 2and a base plate 9 and, as shown in FIG. 14C, the magnetic headsupporting section 5 is connected, via a boss section 10 formed in thebase plate 9, to a holder arm 11 in a caulked state.

Base sections of a plurality of holder arms 11 to hold the magnetic headsupporting section 5, as shown in FIG. 14C, constitutes integrally anarm block 12. The arm block 12 holding the magnetic head supportingsection 5 is mounted through a rotary bearing section 14 in a magneticdisk device in a manner that it can rotate freely.

As shown in FIG. 15, a movable coil 13 is mounted to an end portion ofthe arm block 12. A voice coil motor (VCM) is composed of the movablecoil 13 and an external fixing magnetic circuit 15 mounted in themagnetic disk device. Such a voice coil motor is adapted to apply apredetermined driving current to the movable coil 13 to generate adriving force which drives the arm block 12 holding the magneticsupporting section 5 to be rotated on a circular arc track in a seekdirection (that is, in a direction of a diameter of the magnetic disk)and also drives a magnetic head 1 to perform a positioning operation tofind a target track on the magnetic disk (this method is called a“rotary actuator method”).

The positioning operation described herein includes a seek operation (ora tracking operation) to move the magnetic head 1 from an arbitrarytrack place to a target place and a follow operation to cause themagnetic head 1 to follow the target track.

However, the conventional magnetic head positioning mechanism, since aplurality of magnetic heads 1 is driven simultaneously by one VCMmounted therein, cannot provide sufficient positioning accuracy,especially the track following accuracy in the follow operationsrequired in high TPI positioning devices in which the positioningaccuracy of 0.1 μm or less is needed.

To solve this problem, development of a two-stage actuator type magnetichead positioning mechanism is pursued in which each of the magneticheads 1 is individually driven regardless of driving of the arm block 12by the VCM.

Japanese Patent Application No. Hei10-355697 with a title “Magnetic headslider positioning mechanism” applied by the present inventor and beingpending now, discloses an example of an HGA (Head Gimbal Assembly)two-stage actuator type magnetic head positioning mechanismincorporating piezo-electric elements as shown in FIGS. 16A and 16B.

In the disclosed HGA driving two-stage actuator type magnetic headpositioning mechanism, as shown in FIGS. 16A and 16B, a magnetic headsupporting section 5 is connected to a tip of an actuator spring 8 and abase portion of the actuator spring 8 is fixed to a holder arm (notshown). A pair of piezo-electric elements 16 is disposed, both being inparallel to each other, on the actuator spring 8, with a center axis ofthe actuator spring 8 interposed and, while a magnetic head is followinga track, a predetermined voltage (for example, ±30V) is alternatelyapplied to each of the piezo-electric elements 16 to generate a drivingforce which makes flexible both a center spring 18 and side springs 19mounted on the actuator spring 8, as shown in FIGS. 17A and 17B, anddrives the magnetic head supporting section 5 to be rotated minutely ina track direction.

At this point, the piezo-electric elements 16 each being mounted so asto straddle each of driving voids 17, 17, with an “A” portion of eachpiezo-electric element 16 positioned on a holder arm side (not shown)being fixed as a fixing end, is adapted to expand and shrink a “B”portion of each piezo-electric element 16 positioned on a magnetic headside to make two side springs 19 flexible, which moves minutely themagnetic head supporting section 5 by using a “C” portion in thevicinity of the center spring 18 as a rotation axis.

However, the above HGA driving two-stage actuator type magnetic headpositioning mechanism has shortcomings in that, since the driving voidsmust be mounted on distorting operation portions of the piezo-electricelements 16, not only stiffness in a vertical direction is greatlyimpaired but also shock-resistance and load/unload durability aredecreased. Though required stiffness in the vertical direction can beobtained by changing a geometry of driving spring sections including thecenter spring 18 or side springs 19 and/or by increasing thickness of aspring plate used for the center spring 18 or the side springs 19 toimprove the spring stiffness, it also causes an increase in in-facerotary stiffness, thus leading to a great driving loss at a fineactuator section and to a narrow driving stroke of the magnetic head 1.This makes it difficult to achieve sufficient positioning accuracy andto apply the technology to high TPI positioning devices.

Moreover, another type of the HGA driving two-stage actuator typemagnetic head positioning mechanism using piezo-electric elements isavailable in which driving voids are not formed in the driving portion,as shown in FIG. 18A. This conventional HGA driving two-stage actuatortype magnetic head positioning mechanism is so constructed thatpiezo-electric elements 16 are floated from an actuator spring 8position due to a thickness of an adhesive layer 24 used to stick bothends of the piezo-electric element 16 to the actuator spring 8, whichserves to avoid interference between expanding and shrinking portions ofthe piezo-electric elements 16 and the actuator spring 8, as shown inFIG. 18B. However, since the thickness of the adhesive layer 24 is assmall as about 10 μm, there are risks of contact of the piezo-electricelements 16 with the actuator spring 8 and/or a short-circuit betweenthem.

Furthermore, a same trade-off between the stiffness in a verticaldirection and the rotary stiffness occurs structurally in the actuatorspring 8 as in a case of the example shown in FIG. 16. That is, ifstiffness of a driving spring section is increased to ensureshock-resistance and load/unload durability of the actuator spring 8, adriving loss becomes greater, thus making it impossible to obtain asufficient moving range, while, if the stiffness of the driving springsection is decreased to minimize the driving loss, it is impossible toensure shock-resistance and/or load/unload durability.

In the conventional single-actuator-type magnetic head positioningmechanism as shown in FIGS. 14A, 14B, 14C and 15, when the magnetic headsupporting section 5 is connected to the holder arm 11, a method is usedin which a boss section 10 formed in the load beam 4 is fitted into amounting hole formed in the holder arm 11 and a swage is inserted withpressure and then caulking is performed. This is because the magnetichead supporting section 5 can be easily positioned and a sufficientconnection strength can be obtained. This method is also used widely asa mounting method being excellent in assembly workability, in a case ofcombining the swage insertion with pressure with application of theadhesive, because a leak of the adhesive to positioning jigs can beeffectively prevented by the boss section serving as a wall against theleak.

At this point, since press forming is applied to the boss working, thickmaterials with plasticity are used. Since the load beam 4 used toproduce a pressing load has to be constructed of thin materials withtoughness, the boss section 10 formed in a base plate made frommaterials with plasticity, as shown in FIG. 14A, is junctionedintegrally to the load beam 4, a whole of which is connected to theholder arm 11.

In the method of mounting the magnetic head supporting section 5 for theHGA driving two-stage actuator type magnetic head positioning mechanismas shown in FIG. 14A, since the actuator spring 8 having the drivingspring section has to be constructed of thin plates with toughness, thepress forming is not performed directly on the boss section 10.Therefore, the base plate 9 having the boss section 10 is prepared as aseparate member and then the base plate 9 is integrally junctioned tothe actuator spring 8, the whole of which is then connected to theholder arm 11. In this method, however, due to an increased number ofassembled parts, productivity of the positioning device is decreased anddue to increased thickness of the fine actuator section, mounting of thepositioning mechanism among narrow plates or parts in a small magneticdisk is made difficult.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the present invention toprovide a two-stage actuator type magnetic head positioning mechanismcapable of providing excellent stiffness of an actuator spring in avertical direction without an increase in its rotary stiffness andcapable of ensuring shock-resistance and load/unload durability withoutsacrificing a driving stroke of a magnetic head at a fine actuatorsection. It is another object to provide the two-stage actuator typemagnetic head positioning mechanism which can make it easy to mount thefine actuator section among narrow plates of arm blocks and which canserve to miniaturize a magnetic disk. It is still another object toprovide the two-stage actuator type magnetic head positioning mechanismhaving a sufficient track following capability being suitable tosmall-sized high TPI positioning devices and high reliability of a lifeof a positioning device and of external shock-resistance.

According to a first aspect of the present invention, there is provideda two-stage actuator type magnetic head positioning mechanism including:

a plurality of fine actuator sections which minutely drives, by using apair of piezo-electric elements mounted in the fine actuator sections, amagnetic head supporting section adapted to support a slider on which amagnetic head is attached;

a plurality of holder arms to support each of the fine actuatorsections;

an arm block formed by integrally unifying the plurality of holder arms;and

a voice coil motor to drive the arm block;

whereby the fine actuator section is composed of an actuator spring madefrom one thin steel plate and a base plate made from one thick steelplate, both of which overlap each other, and wherein a driving springsection being connected to the magnetic head supporting section ismounted on the actuator spring and, in a vicinity of the driving springsection, a pair of driving voids to absorb vibration of the magnetichead supporting section and extension/shrinkage of the piezo-electricelements is formed in a state being symmetrical to right and left withrespect to a center axis of the actuator spring and wherein both endportions of the pair of piezo-electric elements are connected to themagnetic head supporting section and to the actuator spring in a mannerthat the end portions straddle each of the driving voids and wherein thebase plate is junctioned to one face of the actuator spring in a mannerthat the base plate covers the pair of driving voids.

By configuring as above, a seek operation for positioning of themagnetic head is performed by vibrating a whole arm block using thevoice coil motor, and accurate positioning operation of the magnetichead and/or a following operation are performed by applying a voltagealternately to each of the pair of piezo-electric elements to expand orshrink the piezo-electric elements which causes the actuator spring tobe made flexible and the magnetic head supporting section to vibrate.Since the base plate composed of the thick steel plate is Functioned tothe actuator spring in a manner that it covers the driving voids, evenif sufficient driving voids are formed in the actuator spring, thestiffness of the actuator spring in a vertical direction,shock-resistance and load/unload durability can be fully ensured. Thus,both excellent stiffness in the vertical direction and satisfactorydriving stroke in a direction of head driving can be simultaneouslyachieved in the magnetic head supporting section.

In the foregoing, a preferable mode is one wherein the base plate isopened at a place where the base plate and the magnetic head supportingsection overlap each other and is Functioned to the actuator spring in amanner that the base plate surrounds external edges of the drivingspring section of the actuator spring.

By configuring as above, interference among the base plate, drivingspring section and magnetic head supporting section can be prevented anda resistance in a head driving direction in the magnetic head supportingsection can be reduced, thus providing further more accuratepositioning.

Also, a preferable mode is one wherein the driving spring section of theactuator spring is composed of a short plate spring and of a pair ofside springs made from long plate springs and wherein a center spring isdisposed on the center axis of the actuator spring while each of theside springs is disposed, with the center spring interposed between theside springs, in a direction being intersected almost at right angles tothe center axis of the actuator spring and wherein the base plate isFunctioned to the actuator spring, at least, at a root area of thecenter spring and the side springs.

By configuring as above, the base plate is junctioned to the actuatorspring at the root area of the center spring and side springs, that is,at a place where stresses centralize most in the actuator spring, thestiffness of the actuator spring in the vertical direction can beimproved and deformation of the actuator spring can be prevented.

Also, a preferable mode is one wherein the pair of driving voids toabsorb vibration of the magnetic head supporting section andextension/shrinkage of the piezo-electric elements is formed at bothsides of a mounting position of the magnetic head supporting section ina state being symmetrical to the right and left with respect to thecenter axis of the actuator spring and wherein each of the pair ofpiezo-electric elements is connected to the magnetic head supportingsection and to the actuator spring in a manner that each of thepiezo-electric elements straddles each of the driving voids along bothsides of the mounting position of the magnetic head supporting sectionand the driving spring section is mounted between the actuator springand the magnetic head supporting section.

By configuring as above, driving voids are formed on both sides of themounting position of the magnetic head supporting section andpiezo-electric elements are mounted along both sides of the mountingposition of the magnetic head supporting section in a manner that thepiezo-electric elements straddle the driving voids. Since the baseportion of the mounting position of the magnetic head supportingsection, driving voids and piezo-electric elements are thus arranged allin a transverse direction with respect to the center axis of theactuator spring, an overall size of the magnetic head supportingsection, its length in particular, can be reduced greatly.

Also, a preferable mode is one wherein the driving spring section of theactuator spring is composed of the center spring made from one shortplate spring and the pair of side springs made from long plate springsand wherein the center spring is connected to the magnetic headsupporting section and to the actuator spring on the center axis of theactuator spring at an end portion of the magnetic head supportingsection being nearer to the holder arm while each of the side springs isconnected to the magnetic head supporting section and to the actuatorspring in a manner that each of the side springs straddles each of thedriving voids and in a manner that each of the side springs intersectsalmost at right angles to each of the piezo-electric elements.

By configuring as above, elastic deformation of the side spring causesthe magnetic head supporting section to vibrate around the center springdisposed at an end portion of the magnetic head supporting section beingnearer to the holder arm. Thus, since the magnetic head supportingsection is able to vibrate over a long span, movable range of themagnetic head mounted at a tip of the magnetic head supporting sectionis made larger, providing stable positioning of the magnetic head.

Also, a preferable mode is one wherein a part of the base plate on whichthe magnetic supporting section is laid is separated from a main portionof the base plate in a state in which the separated part of the baseplate is nested in the main portion of the base plate and is junctionedto the magnetic head supporting section and second driving voids beinglaid on other driving voids so that the second driving voids and theother driving voids overlap each other are formed between the portion ofthe base plate separated to be nested in the main portion of the baseplate and the main portion of the base plate and wherein both endportions of each of the pair of piezo-electric elements are connected tothe magnetic head supporting section and to the actuator spring throughthe portion of the base plate separated to be nested in said mainportion of the base plate and the main portion of the base plate in amanner that each of the piezo-electric elements straddles each of thesecond driving voids.

By configuring as above, not only the actuator spring but also baseportion of the magnetic head supporting section can be reinforced by thethick steel plate, thus improving the stiffness of the magnetic headsupporting section in the vertical direction.

Also, a preferable mode is one wherein the pair of driving voids areformed so as to be intersected in a slanting direction in a manner thata distance between the pair of driving voids is increased graduallytoward the magnetic head from the holder arm side.

By configuring as above, since transverse width of the magnetic headsupporting section is made larger toward the center portion of themagnetic head supporting section from the end portion nearer to theholder arm which constitutes a center for vibration of the magnetic headsupporting section, the stiffness of the magnetic head supportingsection can be improved.

Also, a preferable mode is one wherein length of the actuator spring isset so as to end at a tip of the holder arm so that the actuator springbeing junctioned to the base plate and the holder arm do not overlapeach other when the base plate is connected to the holder arm.

By configuring as above, since the base plate and the holder arm overlapeach other only at a connection point between the magnetic headsupporting section and the holder arm, overall thickness can be reducedmore when compared with a case where the actuator spring is inserted,thus making easier implementation of the fine actuator section amongnarrow parts.

Furthermore, a preferable mode is one wherein a boss section is formedon the base plate so that the base plate is connected to the holder arm.

By configuring as above, since the boss section is formed on the baseplate side where plastic working is easier, working is made easy, thusimproving productivity of the positioning device.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, advantages and features of the presentinvention will be more apparent from the following description taken inconjunction with the accompanying drawings in which:

FIG. 1A is a top view showing an overall configuration of a magnetichead positioning mechanism according to a first embodiment of thepresent invention;

FIG. 1B is a side view of the magnetic head positioning mechanismaccording to the first embodiment;

FIG. 2A is a side view showing main components of the magnetic headpositioning mechanism according to the first embodiment of the presentinvention;

FIG. 2B is a back view showing main components of the magnetic headpositioning mechanism according to the first embodiment;

FIG. 3A is a top view of a fine actuator section constituting themagnetic head positioning mechanism according to the first embodiment ofthe present invention;

FIG. 3B is a side view of the fine actuator section constituting themagnetic head positioning mechanism according to the first embodiment;

FIG. 3C is a back view of the fine actuator section constituting themagnetic head positioning mechanism according to the first embodiment ofthe present invention;

FIG. 4A is a diagram showing parts constituting the fine actuatorsection of the magnetic head positioning mechanism according to thefirst embodiment of the present invention;

FIG. 4B is a perspective view showing parts constituting the fineactuator section of the magnetic head positioning mechanism according tothe first embodiment;

FIG. 5A is a diagram showing distribution of stress by vertical load inthe fine actuator section of the magnetic head positioning mechanismaccording to the first embodiment of the present invention;

FIG. 5B is an enlarged diagram showing a part of the stress distributiondiagram of FIG. 5A;

FIG. 5C is a diagram showing transmission characteristics of the fineactuator section in the magnetic head positioning mechanism according tothe first embodiment;

FIG. 6A is atop view of a fine actuator section of a magnetic headpositioning mechanism according to a second embodiment of the presentinvention;

FIG. 6B is a side view of the fine actuator section of the magnetic headpositioning mechanism according to the second embodiment;

FIG. 6C is a back view of the fine actuator section of the magnetic headpositioning mechanism according to the second embodiment;

FIG. 7 is a diagram showing configurations of parts constituting thefine actuator section of the magnetic head positioning mechanism of thesecond embodiment of the present invention;

FIGS. 8A and 8B are sectional side views of the fine actuator sectionexplaining effects attained by the second embodiment;

FIGS. 8C and 8D are sectional side views of configurations of the fineactuator section of the first embodiment used for comparison of effectsof the first embodiment with those obtained by the second embodiment ofthe present invention;

FIG. 9A is a top view of a fine actuator section of a magnetic headpositioning mechanism according to a third embodiment of the presentinvention;

FIG. 9B is a side view of the fine actuator section of the magnetic headpositioning mechanism according to the third embodiment;

FIG. 9C is a back view of the fine actuator section of the magnetic headpositioning mechanism according to the third embodiment;

FIG. 10 is a diagram showing configurations of parts constituting thefine actuator section of the magnetic head positioning mechanism of thethird embodiment of the present invention;

FIG. 11A is a top view of a fine actuator section of a magnetic headpositioning mechanism according to a fourth embodiment of the presentinvention;

FIG. 11B is a side view of the fine actuator section of the magnetichead positioning mechanism according to the fourth embodiment of thepresent invention;

FIG. 11C is a back view of the fine actuator section of the magnetichead positioning mechanism according to the fourth embodiment of thepresent invention;

FIG. 12 is a diagram showing configurations of parts constituting thefine actuator section of the magnetic head positioning mechanism of thefourth embodiment of the present invention;

FIGS. 13A and 13B are top views explaining an operational principle ofthe magnetic head positioning mechanism of the fourth embodiment of thepresent invention;

FIG. 14A is a top view showing a magnetic head supporting sectionconstituting a conventional magnetic head positioning mechanism;

FIG. 14B is a perspective view showing the magnetic head supportingsection of the conventional magnetic head positioning mechanism;

FIG. 14C is a side view showing overall configurations of theconventional magnetic head positioning mechanism;

FIG. 15 is a top view showing main portions of a conventional diskdevice; and

FIG. 16A is a perspective view showing a magnetic head supportingsection of a two-stage actuator type magnetic head positioning mechanismas a related art;

FIG. 16B is an exploded perspective view showing the magnetic headsupporting section in exploded form;

FIGS. 17A and 17B are top views explaining respectively an operationalprinciple of the a two-stage actuator type magnetic head positioningmechanism;

FIG. 18A is a perspective view showing a magnetic head supportingsection of a conventional two-stage actuator type magnetic headpositioning mechanism; and

FIG. 18B is a cross-section view showing the piezo-electric elements andvicinity of the magnetic head supporting section;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Best modes of carrying out the present invention will be described infurther detail using various embodiments with reference to theaccompanying drawings.

First Embodiment

FIG. 1A is a top view showing an overall configuration of a magnetichead positioning mechanism according to a first embodiment of thepresent invention and FIG. 1B is a side view of the magnetic headpositioning mechanism according to the first embodiment. FIG. 2A is aside view showing main components of the magnetic head positioningmechanism according to the first embodiment and FIG. 2B is a back viewshowing main components of the magnetic head positioning mechanismaccording to the first embodiment. FIG. 3A is a top view of a fineactuator section constituting the magnetic head positioning mechanismaccording to the first embodiment, FIG. 3B is a side view of the fineactuator section constituting the magnetic head positioning mechanismaccording to the first embodiment and FIG. 3C is a back view of the fineactuator section constituting the magnetic head positioning mechanismaccording to the first embodiment. FIG. 4A is a diagram showing partsconstituting the fine actuator section of the magnetic head positioningmechanism according to the first embodiment and FIG. 4B is a perspectiveview showing parts constituting the fine actuator section of themagnetic head positioning mechanism according to the first embodiment.

In description, a figure showing a face portion directing to a surfaceof a magnetic medium is defined as the “top view” and the figure showinga face portion existing on an opposite side of the face portiondirecting to the surface of the magnetic medium is defined as the “backview”. Expressions of the top/back views are not related todirectionality shown when the magnetic head positioning device isinstalled. A term “section” represents a unified whole to implement afunction.

As shown in FIGS. 1A and 1B, the magnetic head positioning mechanism ofthe first embodiment is composed of a magnetic head supporting section 5and two-stage type actuator having a fine actuator section 6 containingthe magnetic head supporting section 5 and a course actuator 7. As shownin FIGS. 3A and 3B, the magnetic head supporting section 5 is composedof a floating-type or contact-type slider 2 on which a magnetic head 1is mounted, a gimbal spring 3 to support the slider 2 and a load beam 4to apply pressing power to the slider 2. As shown in FIG. 3C, the loadbeam 4 is integrally formed with an actuator spring 8 composed of onethin steel plate to obtain assembly workability. However, as shown in athird embodiment described later, the load beam 4 may be constructed ina manner that it is a separate part from the actuator spring 8.

The fine actuator section 6, as shown in FIGS. 3A and 3B, is composed ofthe actuator spring 8, piezo-electric elements 16 and a base plate 9.The fine actuator section 6, as shown in FIGS. 2A and 2B, is connectedvia a boss section 10 formed in the base plate 9 to a holder arm 11.Also, as shown in FIG. 3C, the fine actuator section 6 is provided witha FPC (Flexible printed cable).

An arm block (carriage) 12 composed of a plurality of holder arms 11 isprovided with a movable coil 13 on its one end and constitutes a VCM incombination with an external fixing magnetic circuit (not shown) to formthe course actuator 7, as shown in FIGS. 1A and 1B.

As shown in FIGS. 2B and 3C, a pair of cuboid-shaped piezo-electricelements 16 is mounted, each straddling each driving void 17 and with acenter axis of the actuator spring 8 interposed between thepiezo-electric elements, on the actuator spring 8 both being disposed inparallel to each other. As shown in FIG. 4A, a driving spring section 23is formed between the load beam 4 constituting a part of the magnetichead supporting section 5 and the actuator spring 8. Any kind of drivingspring may be used so long as it has structurally low in-face rotarystiffness and high stiffness in its vertical direction. The drivingspring section 23 of the first embodiment is composed of a pair of longI-shaped side springs 19 which are disposed so as to intersect in adirection perpendicular to the center axis of the actuator spring 8 andof one short I-shaped center spring 18 disposed on the center axis ofthe actuator spring 8 (refer to Japanese Patent Application No.Hei10-355697 and FIG. 16B) . Thin plate materials with toughness such asSUS304 or a like are preferably used as materials for the actuatorspring 8 and load beam 4 because properties as a spring material arerequired in this case.

The actuator spring 8 and the base plate 9 are laid in a manner thatthey overlap each other, except portions in which the load arm 4 is laidon the base plate 9 and portions in which the driving spring section 23is mounted. The boss section 10 is formed on the base plate 9, by pressworking, at a connection point with the holder arm 11. To form the baseplate 9, unlike in a case of the actuator spring 8, materials withplasticity are preferably selected to obtain workability at the bosssection 10. The thickness of the base plate 9 is decided based on atradeoff between the height of the boss section 10 and allowablemounting height.

An end portion of the base plate 9 disposed nearer to the magnetic head1 is so constructed that the actuator plate 8 is laid on the base plate9 in a manner that the driving voids 17 formed in the actuator spring 8are covered and that the base plate 9 and actuator spring 8, bothoverlapping each other, surround external edges of the driving springsection 23. When the base plate 9 and actuator spring 8 are junctioned,for example, by a laser spot welding method, welding is carried out notonly on junction positions shown on the base plate 9 as welding points20 around the boss section 10 as shown in FIGS. 3A and 3B, but also onjunction positions shown as welding points 20 in areas of the externaledges of the driving spring section 23, that is, on a root areasurrounding a fixing side of the center spring 18 and side springs 19.

As shown in FIG. 2A, the base plate 9 is disposed on a storage medium 27side and the actuator spring 8 is laid on the base plate 9 andpiezo-electric elements are mounted on the actuator spring 8 (on theholder arm 11 side) . A through hole is formed on a position used toconnect the holder arm 11 on the actuator spring 8 and the boss section10 of the base plate 9 passes through the through hole of the actuatorspring 8 and is fitted into a holder arm mounting hole 28.

If there is sufficient room for mounting parts at the fine actuatorsection 6, it is possible to mount the actuator spring 8 on the storagemedium 27 side and the base plate 9 on the holder arm 11 side. However,in this case, since the piezo-electric elements 16 are to be connectedin an opposed direction to the storage medium 27, there is the risk of aphysical contact or electric short-circuit between the storage medium 27and piezo-electric elements 16.

When the two-stage actuator described above drives minutely the magnetichead 1 to a seek direction, a voltage is applied to each of thepiezo-electric elements 16 mounted on the actuator spring 8 in a mannerthat each of them has an opposite phase to make the driving springsection 23 flexible and to obtain a fine rotation of the magnetic headsupporting section 5. At this point, as shown in FIG. 2B, each of thepiezo-electric elements 16, with an “A” portion of each piezo-electricelement 16 positioned on a holder arm side (not shown) being fixed tothe actuator spring 8 as a fixing end, is adapted to expand and shrink a“B” portion of each piezo-electric element 16 serving as a driving endfor each piezo-electric element 16 disposed on the magnetic head side,which causes two side springs 19 to be displaced using a “C” portion asa rotation axis which also corresponds positionally to a center of thetwo side springs 19 and then the magnetic head 1 to be driven for trackfollowing operations.

Thus, in the magnetic head positioning mechanism of the embodiment,since the actuator spring 8 and base plate 9 overlap each other on thedriving voids 17 and they surround the edge portion of the drivingspring 23, the area surrounding the driving voids 17 can be reinforced.This allows rotary stiffness of the driving spring 23 to be keptdecreased and stiffness in the vertical direction of the fine actuatorsection 6 to be kept increased.

FIGS. 5A and 5B are diagrams showing distribution of stress obtained bysimulation of the internal stress occurring when a load of about 2.5 gis imposed, with the fine actuator section 6 of the first embodimentbeing fixed at a connection place to the holder arm 11. As is apparentfrom FIG. 5A, a stress of 6×10⁸Pa is generated at a load-bendingposition 4 a of the load beam 4 at the time of loading and unloading,however, there is only a stress of 9×10⁷ at center spring 18 and sidesprings 19 of the actuator spring 8 as shown in FIG. 5B.

FIG. 5C is a simulation diagram showing transmission characteristics atthe magnetic head 1 position obtained when the piezo-electric elements16 are driven, with the fine actuator section 6 of the first embodimentbeing fixed at the connection place to the holder arm 11. In themagnetic head positioning mechanism of the embodiment using the baseplate 9 for reinforcing the area surrounding the driving spring section23, since not only bending stiffness but also torsional stiffness can beincreased in the fine actuator section 6, it is possible to obtainexcellent vibrating characteristics being free from a resonance peakover a wide frequency band (>10 kHz).

Second Embodiment

FIGS. 6A, 6B and 6C are top, side and back views of a fine actuatorsection, respectively, of a magnetic head positioning mechanism of asecond embodiment of the present invention. FIG. 7 is a diagram showingconfigurations of parts constituting the fine actuator section of themagnetic head positioning mechanism of the second embodiment. FIGS. 8Aand 8B are sectional side views of the fine actuator section explainingeffects attained by the second embodiment and FIGS. 8C and 8D aresectional side views of the fine actuator section of the firstembodiment used for comparison of effects of the first embodiment withthose obtained by the second embodiment. Configurations of the secondembodiment are almost same as those of the first embodiment except thefine actuator section. In the second embodiment, same reference numbersas for the first embodiment are assigned to parts and sections havingsame functions as in the first embodiment.

In the first embodiment, actuator spring 8 and base plate 9 constitutinga fine actuator section 6 are laid in a manner so that they overlap eachother and, as shown in FIG. 8C, a boss section 10 of the base plate 9 ispassed through a through hole formed in the actuator spring 8 and thenis fitted into a holder arm mounting hole 28 of holder arm 11. However,in the above configurations of the first embodiment, since height (h1)of the boss section 10 as shown in FIG. 8D is structurally reduced byplate thickness of the actuator spring 8 and thus height of fitting theboss section 10 into the holder arm mounting hole 28 of the holder arm11 is also made smaller, sufficient fitting strength cannot be obtained,causing the risk of interfering with satisfactory assembling of the fineactuator section 6.

To solve this problem, as already described above, assembling method isavailable in which the actuator spring 8 is mounted on a storage medium27 side and the base plate 9 is junctioned to the holder arm 11.However, in this method, since the piezo-electric elements 16 also haveto be mounted on the storage medium 27 side, unless the magnetic headpositioning mechanism has sufficient mounting height at its fineactuator section 6, it is difficult to ensure a margin of safety againstelectrical short-circuit and/or physical contact between thepiezo-electric elements 16 and the storage medium 27.

Thus, according to the second embodiment, the portion in which theactuator spring 8 and the holder arm 11 overlaps in the first embodimentis removed as shown in FIGS. 6B and 6C and, when the actuator spring 8is laid on the base plate 9 having the boss section 10, laser spotwelding is carried out only on portions surrounding driving voids 17which are shown as jwelding points 20, as shown in FIGS. 6A and 6C.

Since an external area of a driving spring section 23, that is, a rootarea of a center spring 18 and side springs 19 is reinforced by the baseplate 9 as in the first embodiment, it is possible to ensure sufficientbending and torsional stiffness in the fine actuator section 6.

Moreover, as shown in FIG. 8B, in the configurations according to thesecond embodiment, since the actuator spring 8 does not contact theholder arm 11, a sufficient height (h2) of the boss section 10 can beensured after it is connected to the holder arm 11 and thus excellentfitting strength can be obtained.

Third Embodiment

FIGS. 9A, 9B and 9C are top, side and back views of a fine actuatorsection, respectively, of a magnetic head positioning mechanism of athird embodiment of the present invention. FIG. 10 is a diagram showingconfigurations of parts constituting the fine actuator section of themagnetic head positioning mechanism of the third embodiment. In thethird embodiment, same reference numbers as for the first embodiment areassigned to parts and sections having same functions as in the firstembodiment.

In the first and second embodiments, a load beam 4 constituting a fineactuator section 6 is integrally formed with an actuator spring 8composed of one thin steel plate to obtain assembly workability. In thethird embodiment, as shown in FIG. 10, the actuator spring 8 and loadbeam 4 are separately formed and assembled independently.

In this method, though assembling workability is impaired somewhat dueto increased numbers of parts, there are still advantages in that theload beam 4 and the conventional magnetic head supporting section 5,each existing as a separate unit, can be used as they are without needsfor integral formation. The load beam 4 can be simply mounted via acaulking hole 22 formed in the actuator spring 8, by using a rivet or alike, on the actuator spring 8.

An overall configuration of the fine actuator section 6 of the thirdembodiment achieved after being assembled is the. same as those in thefirst and second embodiments as shown in FIGS. 9A, 9B and 9C.

Fourth Embodiment

FIGS. 11A, 11B and 11C are top, side and back views of a fine actuatorsection, respectively, of a magnetic head positioning mechanism of afourth embodiment of the present invention. FIG. 12 is a diagram showingconfigurations of parts constituting the fine actuator section of themagnetic head positioning mechanism of the fourth embodiment. In thefourth embodiment, same reference numbers as for the first embodimentare assigned to parts and sections having same functions as in the firstembodiment.

As shown in FIGS. 11A and 11C, a fine actuator section 6 of the fourthembodiment is composed of an actuator spring 8, piezo-electric elements16 and a base plate 9. The actuator spring 8 composed of one steel plateis integrally formed with a load beam 4. A gimbal spring 3 holding aslider 2 and the load beam 4 constitute, in combination, a magnetic headsupporting section 5. A pair of driving voids 17 is formed on theactuator spring 8 on both sides of a mounting place of the load beam 4in a state being symmetrical right and left with respect to a centeraxis of the actuator spring 8. The driving voids 17 are formed so as tobe intersected in a slanting direction in a manner that a distancebetween the driving voids 17 is increased gradually toward a magnetichead 1 from a holder arm 11 side and, as a result, a transverse width ofthe load beam 4 constituting the magnetic head supporting section 5 islargest at a central position in a longitudinal direction.

As shown in FIG. 12, a driving spring section 23 composed of one centerspring 18 and a pair of side springs 19 is formed on the actuator spring8. The center spring 18 is composed of one short I-shaped plate springwhich connects the load beam 4 to the actuator spring 8 at an end, beingnearer the holder arm 11, of the load beam 4 constituting a part of themagnetic head supporting section 5. Each of the side springs 19 composedof long I-shaped springs is mounted, straddling the driving void 17, ina direction intersecting at right angles with respect to a longitudinaldirection of the driving void 17 and connects the load beam 4 and theactuator spring 8.

The base plate 9 and the actuator spring 8 are laid so that they overlapeach other. On the base plate 9 is formed second driving voids 26 whichare equivalent to the driving voids 17 formed in the actuator spring 8.The base plate 9 is divided by the second driving voids 26 into aninternal part and an external part. The external part becomes a mainpart 9 a of the base plate 9 and an inner part becomes a driving stage 9b in a state in which the inner part is nested.

A base bridge section 25 adapted to connect the main part 9 a of thebase plate 9 to the driving stage 9 b is left in a state shown in FIG.12 to obtain easiness for working and assembly and to ensure accuracyuntil welding on each part is complete.

As shown in FIG. 1C, the main part 9 a of the base plate 9 is junctionedto the actuator spring 8 by carrying out a laser spot welding at weldingpoints 20. The driving stage 9 b is also junctioned to the load beam 4by carrying out laser spot welding at two or more welding points 20.After the above welding processes are complete, a pair of thepiezo-electric elements 16 is disposed, straddling the second drivingvoids 26 in a longitudinal direction, on the main part 9 a of the baseplate 9 and the driving stage 9 b along both sides of the mountingposition for the load beam 4. As shown in FIG. 11C, both sides of eachof the piezo-electric elements 16 are junctioned to the main part 9 a ofthe base plate 9 and the driving stage 9 b and finally the base bridgesection 25 is cut in a manner shown in FIG. 1C.

Since the side spring 19, as described above, is mounted so as tointersect at right angles to the longitudinal direction of the drivingvoids 17 formed along the mounting position for the load beam 4 andsince each of the piezo-electric elements 16 is mounted along thelongitudinal direction of the second driving void 26, that is, along thelongitudinal direction of the driving void 17, the side spring 9 and thepiezo-electric element 16, as a result, almost intersect each other atright angles.

Next, an operation principle of the magnetic head positioning mechanismof the fourth embodiment will be described by referring to FIGS. 13A and13B. FIG. 13A is a top view of the fine actuator section of the fourthembodiment, seen from a storage medium side, to explain its operationand FIG. 13B is a top view of the fine actuator section seen from aholder arm side.

When driving power is applied to the pair of the piezo-electric elements16 mounted, with a center axis of the main part 9 a of the base plate 9being interposed between the piezo-electric elements 16, in a mannerthat each of them has an opposite phase, each of the piezo-electricelement 16, an “A” portion of which is fixed to the base plate 9 beingnearer to the magnetic head 1, expands a “B” portion of thepiezo-electric element 16 which is connected, straddling the drivingvoid 26, to the driving stage 9 b and makes flexible the side spring 19and the center spring 18, which causes the magnetic head supportingsection 5 together with the driving stage 9 b to be rotated using a “C”as a rotation center axis and causes the magnetic head 1 to performfollowing operation on a track. FIG. 13B shows an example of operationsin which the piezo-electric element 16 placed in a lower position isexpanded and the piezo-electric element 16 placed in a higher positionis shrunk.

In the magnetic head positioning mechanism of the embodiment, as shownin FIGS. 13A and 13B, since the driving rotation center “C” position ofthe magnetic head supporting section 5 can be disposed apart from themagnetic head 1 as much as possible, by increasing a driving multiplyingfactor, that is, an amount of driving of the magnetic head 1 to anamount of distortion of the piezo-electric element 16, a wide movablerange for the magnetic head 1 can be ensured, thus providingsatisfactory magnetic head 1 positioning accuracy.

Moreover, according to the embodiment, since the fine actuator section 6is so constructed that the side springs 19 are mounted so as to straddlethe driving voids 17 and second driving void 26 and the piezo-electricelements 16 are overlaid on the side spring 19, the driving springsection 23 can be designed to be compact to keep its rotary stiffnessdecreased and can be reinforced by the main part 9 a of the base plate 9and the driving stage 9 b to ensure sufficient stiffness, thus providingexcellent shock-resistance and load/unload durability of the magnetichead positioning mechanism.

As described above, according to the present invention, since themagnetic head positioning mechanism is so configured that the base platecomposed of the thick steel plate is incorporated so as to cover thedriving voids formed in the actuator spring, it is possible to ensurestiffness of the actuator spring in the vertical direction,shock-resistance and load/unload durability without increased stiffnessof the driving spring section even if sufficient driving voids areprovided in the actuator spring and to obtain satisfactory drivingstroke to the magnetic head driving direction and excellent positioningaccuracy.

Also, according to the present invention, since the magnetic headpositioning mechanism is so constructed that the base plate isjunctioned to the actuator spring, with the portion of the base plate onthe magnetic head supporting section being opened and in the manner thatthe driving spring section of the actuator spring is surrounded,interference among the driving spring section, the magnetic headsupporting section and the base plate can be surely prevented, thusreducing resistance in the direction of the magnetic head driving in themagnetic head supporting section and providing more accuratepositioning.

Moreover, according to the present invention, since the magnetic headpositioning mechanism is so constructed that the base plate beingoverlaid by the actuator spring is junctioned to the actuator spring atthe root area of the center spring and side spring constituting thedriving spring section, that is, at a place where stresses centralizemost in the actuator spring, the stiffness of the actuator spring in thevertical direction is improved and deformation of the actuator springcan be prevented effectively.

Also, according to the present invention, since the magnetic headpositioning mechanism is so constructed that the driving voids to absorbvibration of the magnetic head supporting section andextension/shrinkage of the piezo-electric elements are formed on bothsides of the mounting place of the magnetic head supporting section inthe state being symmetrical to the right and left with respect to thecenter axis of the actuator spring and the piezo-electric elements aremounted so as to straddle these driving voids, the mounting base of themagnetic head supporting section, the driving voids, and piezo-electricelements can be arranged in transverse direction with respect to thecenter axis of the actuator spring, thus greatly reducing the overallsize of the magnetic head supporting section, its strength inparticular. In this case, by mounting one of the plate springsconstituting the driving spring section of the actuator spring at theend being nearer to the holder arm in the magnetic head supportingsection, the magnetic head supporting section can be vibrated, over along span, around the end portion being nearer to the holder arm of themagnetic head supporting section. This allows moving range of themagnetic head attached to the end of the magnetic head supportingsection to be made larger, thus providing stable magnetic headpositioning.

Also, according to the present invention, since the magnetic headpositioning mechanism is so constructed that the part of the base plateon which the magnetic head supporting section is laid is separated fromthe main part of the base plate in the state in which the separated partof the base plate is nested in the main part of the base plate and isjunctioned to the magnetic head supporting section, the base portion ofthe magnetic head supporting section is reinforced by the thick steelplate, thus serving to improve the stiffness of the magnetic headsupporting section in the vertical direction.

Moreover, according to the present invention, since the magnetic headpositioning mechanism is so constructed that the driving voids areformed so as to be intersected in the slanting direction in the mannerthat the distance between the driving voids is increased graduallytoward the magnetic head from the holder arm side, the transverse widthof the magnetic head supporting section at the center in thelongitudinal direction can be made larger, thus ensuring the stiffnessof the magnetic supporting section even when it is vibrated in the longspan.

Also, according to the present invention, since the magnetic headpositioning mechanism is so constructed that the length of the actuatorspring is so set that the actuator spring and the holder arm do notoverlap when the base plate is connected to the holder arm, it ispossible to make the fine actuator section thinner, which enables thefine actuator section to be mounted even among narrow plates in thepositioning device, thus serving to miniaturize the entire magneticdisk.

Furthermore, according to the present invention, the magnetic headpositioning mechanism is so constructed that the boss section used toconnect the fine actuator section to the holder arm is mounted on thebase plate side where the base plate is junctioned to the actuatorspring and where plastic working can be carried out easily, working ofthe boss section is made easier and productivity of the positioningdevice can be improved and, since the positioning mechanism is soconfigured that the actuator spring is not interposed between the baseplate and holder arm, the boss section of the base plate is providedwith sufficient amounts of projection, thus improving the junctionstrength between the fine actuator section and the holder arm.

It is apparent that the present invention is not limited to the aboveembodiments but may be changed and modified without departing from thescope and spirit of the invention.

1-16. (canceled)
 17. A two-stage actuator type magnetic head positioningmechanism comprising: a plurality of fine actuator sections whichminutely drives, by a pair of piezo-electric elements mounted in saidfine actuator sections, a magnetic head supporting section adapted tosupport a slider on which a magnetic head is attached; a plurality ofholder arms to support each of said fine actuator sections; an arm blockformed by integrally unifying said plurality of holder arms; and a voicecoil motor to drive said arm block; wherein said fine actuator sectionis composed of an actuator spring made from one thin steel plate and abase plate made from one thick steel plate, wherein a driving springsection being connected to said magnetic head supporting section ismounted on said actuator spring and, in a vicinity of said drivingspring section, a pair of driving voids to absorb vibration of saidmagnetic head supporting section and extension/shrinkage of saidpiezo-electric elements along a longitudinal axis is formed in a statebeing symmetrical right and left and parallel with respect to alongitudinal center axis of said actuator spring, wherein both endportions of said pair of piezo-electric elements are connected to saidmagnetic head supporting section and to said actuator spring in a mannersuch that said end portions straddle each of said driving voids, andwherein said base plate is junctioned to one face of said actuatorspring in a manner such that said base plate covers said pair of drivingvoids, and only portions of said actuator spring and said base platesurrounding said pair of driving voids are laser spot welded.
 18. Thetwo-stage actuator type magnetic head positioning mechanism according toclaim 17, wherein said base plate is opened at a place where said baseplate and said magnetic head supporting section overlap each other andis junctioned to said actuator spring in a manner such that said baseplate surrounds external edges of said driving spring section of saidactuator spring.
 19. The two-stage actuator type magnetic headpositioning mechanism according to claim 17, wherein said driving springsection of said actuator spring is composed of a center spring made froma short plate spring and of a pair of side springs made from long platesprings, wherein said center spring is disposed on said center axis ofsaid actuator spring while each of said side springs is disposed, withsaid center spring interposed between said side springs, in a directionbeing intersected almost at right angles to said center axis of saidactuator spring, and wherein said base plate is junctioned to saidactuator spring, at least, at a root area of said center spring and saidside springs.
 20. The two-stage actuator type magnetic head positioningmechanism according to claim 18, wherein said driving spring section ofsaid actuator spring is composed of a center spring made from a shortplate spring and of a pair of side springs made from long plate springs,wherein said center spring is disposed on said center axis of saidactuator spring while each of said side springs is disposed, with saidcenter spring interposed between said side springs, in a direction beingintersected almost at right angles to said center axis of said actuatorspring, and wherein said base plate is junctioned to said actuatorspring, at least, at a root area of said center spring and said sidesprings.
 21. The two-stage actuator type magnetic head positioningmechanism according to claim 17, wherein said pair of driving voids toabsorb vibration of said magnetic head supporting section andextension/shrinkage of said piezo-electric elements is formed at bothsides of a mounting position of said magnetic head supporting section insaid state being symmetrical right and left with respect to said centeraxis of said actuator spring, and wherein each of said pair ofpiezo-electric elements is connected to said magnetic head supportingsection and to said actuator spring in a manner such that each of saidpiezo-electric elements straddles each of said driving voids along bothsides of said mounting position of said magnetic head supportingsection, and said driving spring section is mounted between saidactuator spring and said magnetic head supporting section.
 22. Thetwo-stage, actuator type magnetic head positioning mechanism accordingto claim 18, wherein said pair of driving voids to absorb vibration ofsaid magnetic head supporting section and extension/shrinkage of saidpiezo-electric elements is formed at both sides of a mounting positionof said magnetic head supporting section in said state being symmetricalright and left with respect to said center axis of said actuator spring,and wherein each of said pair of piezo-electric elements is connected tosaid magnetic head supporting section and to said actuator spring in amanner such that each of said piezo-electric elements straddles each ofsaid driving voids along both sides of said mounting position of saidmagnetic head supporting section, and said driving spring section ismounted between said actuator spring and said magnetic head supportingsection.
 23. The two-stage actuator type magnetic head positioningmechanism according to claim 21, wherein said driving spring section ofsaid actuator spring is composed of said center spring made from oneshort plate spring and a pair of side springs made from long platesprings, and wherein said center spring is connected to said magnetichead supporting section and to said actuator spring on said center axisof said actuator spring at an end portion of said magnetic headsupporting section being nearer to said holder arm while each of saidside springs is connected to said magnetic head supporting section andto said actuator spring in a manner such that each of said side springsstraddles each of said driving voids and in a manner such that each ofsaid side springs intersects almost at right angles to each of saidpiezo-electric elements.
 24. The two-stage actuator type magnetic headpositioning mechanism according to claim 22, wherein said driving springsection of said actuator spring is composed of said center spring madefrom one short plate spring and a pair of side springs made from longplate springs, and wherein said center spring is connected to saidmagnetic head supporting section and to said actuator spring on saidcenter axis of said actuator spring at an end portion of said magnetichead supporting section being nearer to said holder arm while each ofsaid side springs is connected to said magnetic head supporting sectionand to said actuator spring in a manner such that each of said sidesprings straddles each of said driving voids and in a manner such thateach of said side springs intersects almost at right angles to each ofsaid piezo-electric elements.
 25. The two-stage actuator type magnetichead positioning mechanism according to claim 21, wherein said pair ofdriving voids are formed so as to be intersected in a slanting directionin a manner that a distance between said pair of driving voids isincreased gradually toward said magnetic head from said holder arm side.26. The two-stage actuator type magnetic head positioning mechanismaccording to claim 22, wherein said pair of driving voids are formed soas to be intersected in a slanting direction in a manner that a distancebetween said pair of driving voids is increased gradually toward saidmagnetic head from said holder arm side.
 27. The two-stage actuator typemagnetic head positioning mechanism according to claim 21, whereinlength of said actuator spring is set so as to end at a tip of saidholder arm so that said actuator spring being junctioned to said baseplate and said holder arm do not overlap each other when said base plateis connected to said holder arm.
 28. The two-stage actuator typemagnetic head positioning mechanism according to claim 22, whereinlength of said actuator spring is set so as to end at a tip of saidholder arm so that said actuator spring being junctioned to said baseplate and said holder arm do not overlap each other when said base plateis connected to said holder arm.
 29. The two-stage actuator typemagnetic head positioning mechanism according to claim 17, wherein aboss section is formed on said base plate so that said base plate isconnected to said holder arm.
 30. The two-stage actuator type magnetichead positioning mechanism according to claim 18, wherein a boss sectionis formed on said base plate so that said base plate is connected tosaid holder arm.
 31. A two-stage actuator type magnetic head positioningmechanism comprising: a plurality of fine actuator sections whichminutely drives, by a pair of piezoelectric elements mounted in saidfine actuator sections, a magnetic head supporting section adapted tosupport a slider on which a magnetic head is attached; a plurality ofholder arms to support each of said fine actuator sections; an arm blockformed by integrally unifying said plurality of holder arms; and a voicecoil motor to drive said arm block; wherein said fine actuator sectionseach are composed of an actuator spring made from one thin steel plateand a base plate made from one thick steel plate, wherein a drivingspring section being connected to said magnetic head supporting sectionis mounted on said actuator spring and, in a region of said actuatorspring within a vicinity of said driving spring section, a pair ofdriving voids to absorb vibration of said magnetic head supportingsection and extension/shrinkage of said pair of said piezo-electricelements along a longitudinal axis is formed in a state beingsymmetrical right and left and parallel with respect to a longitudinalcenter axis of said actuator spring, wherein said piezo-electricelements each are connected at one end portion thereof to said magnetichead supporting section, and at another end portion thereof to saidactuator spring in a manner such that said piezo-electric elements eachstraddle the corresponding driving void, wherein a boss section isformed on only said base plate so that only said base plate is fixed tosaid holder arm, wherein said base plate and said actuator springoverlap each other except, at least, a place where said boss section isformed in said base plate and in a manner such that said base platecovers said pair of said driving voids, and said actuator spring andsaid base plate are laser spot-welded in the overlapping portions and ina manner such that said base plate is junctioned to one face of saidactuator spring.
 32. The two-stage actuator type magnetic headpositioning mechanism according to claim 31, wherein a length of saidactuator spring is set in a manner such that said actuator spring beingjunctioned to said base plate and said holder arm do not overlap eachother, when said base plate is connected to said holder arm.
 33. Thetwo-stage actuator type magnetic head positioning mechanism according toclaim 31, wherein said base plate is opened at a place where said baseplate and said magnetic head supporting section overlap each other andis junctioned to said actuator spring in a manner such that said baseplate surrounds external edges of said driving spring section of saidactuator spring.
 34. The two-stage actuator type magnetic headpositioning mechanism according to claim 31, wherein said magnetic headsupporting section and said actuator spring being formed separately fromeach other.
 35. The two-stage actuator type magnetic head positioningmechanism according to claim 31,wherein said driving spring section ofsaid actuator spring is composed of a center spring made from a shortplate spring and of a pair of side springs made from long plate springs,wherein said center spring is disposed on said center axis of saidactuator spring while each of said side springs is disposed, with saidcenter spring interposed between said side springs, in a direction beingintersected almost at right angles to said center axis of said actuatorspring, and wherein said base plate is junctioned to said actuatorspring, at least, at a root area of said center spring and said sidesprings.